Angioplasty procedures have gained wide acceptance in recent years as efficient and effective methods for treating types of vascular disease. In particular, angioplasty is widely used for opening stenoses in the coronary arteries, although it is also used for the treatment of stenoses in other parts of the vascular system.
The most widely used form of angioplasty makes use of a dilation catheter which has an inflatable balloon at its distal end. Inflation of the balloon at the site of the occlusion causes a widening of the lumen to reestablish an acceptable blood flow through the lumen.
Often it is desirable to determine the severity of the occlusion in order to properly choose a dilation catheter. Various techniques have been used to determine the severity of the occlusion. One way of determining the severity of the occlusion is to measure pressure both proximal to and distal of the stenosis. Devices that are used for this purpose include catheter-like members with some type of pressure-sensing device incorporated therein. One known device measures the pressure as a function of the deflection of a diaphragm located either the proximal or distal ends of the catheter. Positioning the sensing part of the sensing device at the proximal end of the catheter can introduce measuring inaccuracies due to the catheter length. Positioning the sensing part of the sensing device at the distal end of the catheter requires a sensing device to be made extremely small. Otherwise, the sensing device will impede the blood flow and affect the pressure reading. It is desirable to provide a pressure sensor that is compact so that it can be delivered to narrow sites while having a high degree of accuracy.
An alternative method of determining the severity of an occlusion is to measure blood flow proximal to, across and distal of the stenosis. Several techniques are in use to measure the flow of blood within a patient's vasculature. Doppler ultrasound and dilution techniques can be used to study blood flow in vessels. Hot wire anemometry has been proposed to measure blood flow as well.
The measurement of blood flow in a coronary artery is especially difficult due to the size and location of the vessel. For example, the measurement device must have a very small diameter so that the vessel under study is not occluded during the measurement. Occlusion will distort the flow measurement and can cause ischemia. It is also important that the flow measurement device generate a reproducible and accurate measure of blood flow as a function of time so that the pulsatile nature of the blood flow is revealed.
It would be desirable to make use of both measurement techniques in order to provide the treating physician with as much diagnostic information as possible. The ideal combined pressure and flow measurement apparatus would be accurate, low profile, flexible and have a fast response time. Both the cost and ease of use of the complete system needs to be considered as well to produce a commercially successful product. Presently available devices are not capable of simultaneously meeting these various requirements.